DISTURBANCES OF THETA AND GAMMA OSCILLATIONS IN THE BRAINS WITH PATHOLOGIES PECULAR TO ALZHEIMER'S DISEASE AND TEMPORAL LOBE EPILEPSY

Theta and gamma oscillations registered in the hippocampus and neocortex are necessary for implementation of cognitive brain functions; their violations are revealed in many neurological and psychiatric diseases. Temporal lobe epilepsy (TLE) and Alzheimer's disease (AD) are the most extended forms of neurodegenerative disorders characterized by the loss of cells and progressive alteration of cognitive functions. Now there are still no effective treatments for TLE and AD, and the existing pharmacological medicines can be useful only at early stages of development of diseases, when it is difficult to diagnose them. A great deal has been done with the aim of defining early biomarkers of these diseases; however, there is a great need for the markers that would reflect changes in brain functioning within milliseconds to obtain information on the specific cognitive disturbances peculiar to patients with certain neuropathologies. In this article, we review literature data suggesting that coherent analysis can be a useful approach to early detection of AD and TLE. These data demonstrated the disturbances in interactions of theta-gamma synchronization in the hippocampal, hippocampal-entorhinal, hippocampal-prefrontal and hippocampal-septal networks in the epileptic brain. In the AD models, marked changes were observed in the theta gamma coupling in the subiculum, an output region of the hippocampus. In addition, a decreased theta-gamma coupling between the hippocampus and the parietal cortex as well as between the hippocampus and the prefrontal cortex was also shown. Assimilation of data of the coherent analysis with behavioral assessments can help in early diagnosis of neuropathologies characterized by cognitive deficit.